1. Field of the Invention
The present invention generally relates to a starter with epicycle or planetary gear speed reduction mechanism having an overrunning clutch and, more particularly, it relates to a starter which has an improved overrunning clutch for automotive use.
2. Related Art
In the conventional starter with epicycle gear or planetary gear speed reduction mechanism disclosed in Japanese Utility Model Laid-open Publication No. 52-19528, an overrunning clutch is set or mounted between the outer circumference surface of an internal gear of the epicycle gear reduction mechanism and the inner circumference surface of a casing that acts as the fixing side to store the epicycle gear speed reduction mechanism.
In the conventional structure explained above, with the overrunning clutch being set on the outer circumference of the epicycle gear speed reduction mechanism, any axial direction space for the over running clutch is not required, the dead space is small, and increased manufacturing costs caused by an increase in weight are low. Furthermore, even if a drive transmission portion with a large diameter is required for the high-load overrunning clutch, the outer circumference of the epicycle gear speed reduction mechanism can be used.
However, as the overrunning clutch portion is set on the outer circumference of the epicycle gear speed reduction mechanism, the diameter of the clutch inner member naturally increases, causing the following types of problems. For example, when comparing the starter with the case when the thickness of the clutch inner is the same as the thickness of the clutch inner of the roller-type overrunning clutch set on the starter output shaft, the clutch according to the above publication has the ratio the thickness to the outer diameter of the clutch inner decreases, and the mechanical strength of the clutch inner as a ring drops. The amount that the clutch inner deforms due to the inner radial force applied on the roller contact portion of the clutch inner increases, and thus, the resistance force of the contact surface required for conveying the torque may not be achieved, or a high torque conveyance may not be possible. If the thickness of the clutch inner is secured to resolve this problem, the inner diameter of the internal gear will be determined by the dimensions of the epicycle gears, etc., housed or by the number of teeth due to the speed reduction ratio, so the outer diameter must be increased, and thereby the epicycle gear speed reduction mechanism has a diameter larger than the other parts.
Furthermore, as the clutch outer member (roller cam) is mounted on the front bracket, when the starter is overrun by the engine, the ring gear (clutch inner) rotates to absorb the rotational difference between the pinion gear rotated by the engine and the starter motor so that the overrun rotation is not conveyed to the starter motor. The roller wears is caused because the rollers constantly contact the outer circumference of the clutch inner.
As this overrunning clutch has a structure wherein the rotational force is conveyed when the roller bites, in the small narrow direction, into the wedge-shaped space formed between the cam-shaped groove set on the inner circumference of the bracket with is the fixing side of the clutch outer and inclined circumferentially and the outer circumference of the internal gear of the epicycle gear speed reduction mechanism that is the clutch inner. Therefore, when the starter overruns, the internal gear that acts as the clutch inner are rotated at a high speed, and since these are made of metal and heavy, the inertia energy during rotation is large. If the engine is rapidly changed from the overrun state to the drive state, the impact applied on the other clutch parts increases, an unbalance occurs during rotation, the device may be damaged or an abnormal noise may be heard during drive.